A new datatype, MPI_WCHAR, is added, for the purpose of dealing with international character sets such as Unicode.
MPI_WCHAR is a C type that corresponds to the type wchar_t defined in <stddef.h>. There are no predefined reduction operations for MPI_WCHAR.
The fact that MPI_CHAR is associated with the C datatype
char, which in turn is often used as a substitute for the ``missing''
byte datatype in C makes it most natural to define this as a new datatype
specifically for multi-byte characters.
( End of rationale.)